Cardiac valve prosthesis

ABSTRACT

A prosthesis for a cardiac valve including prosthetic leaflets which are intended to functionally replace the native leaflets of a cardiac valve following the implantation of the cardiac prosthesis. The prosthesis also including a prosthetic member on which there are mounted the prosthetic leaflets and which is intended to take up a stable, predetermined functional configuration in which the prosthetic member and the prosthetic leaflets reproduce the functionally correct configuration for the purpose of the physiological replacement of the native cardiac valve. The prosthetic member is preconfigured so as to move gradually from an altered, temporary functional configuration, in which the prosthetic member has a deformed geometry with respect to the stable, predetermined stable functional configuration, to said stable, predetermined functional configuration.

FIELD OF APPLICATION

The present invention relates to the field of implantable prostheticdevices for the treatment of malfunctions of cardiac valves.

The invention has been developed with particular regard to animplantable prosthetic device which is capable of replacing thephysiological function of a malfunctioning cardiac valve.

TECHNOLOGICAL BACKGROUND

Cardiac valves are organs which preside over the correct functioning ofthe heart as a pump for the generation of blood flow in the circulationsystem of living beings. The main objective thereof involves making theblood flow unidirectional inside the cardiac cavities, being essentialboth in the filling phase of the cavities, known as the diastolic phase,and in the blood discharge phase, known as the systolic phase.

There are four cardiac valves which are present in the human heart. Themost critical, that is to say, those whose malfunction is mainly evidentas a risk of premature death or significant degradation of the qualityof life, are the aortic valve and the mitral valve, both positioned atthe left side of the heart, which is responsible for the peripheralvascularization of all the body. All four cardiac valves can be affectedby two main malfunction types, stenosis and insufficiency, or by acombination of the two. Stenosis is defined as the pathologicalnarrowing of the valve orifice so as to obstruct the passage of theblood through it with the valve open. Valve insufficiency orincompetence is defined, vice versa, as the incapacity of the leafletsof the valve to close completely. The incomplete coaptation of theleaflets therefore leads to the phenomenon of regurgitation, that is tosay, the formation of a backward flow, with the valve closed. Stenosisof the aortic valve and insufficiency of the mitral valve are the valvepathologies which are most widespread in occidental countries.

Insufficiency of a cardiac valve is a malfunction which is hugelyincapacitating for the patient and very onerous for the cardiac muscle.Insufficiency is a particularly serious malfunction for anatrio-ventricular valve, specifically for the mitral valve. Thatmalfunction often triggers a vicious circle which leads to a rapiddeterioration of the pathological outlook. In fact, blood regurgitationthrough the mitral valve inhibits the efficiency of the left ventricle,reducing the volume of oxygenated blood which is effectively dischargedby the heart towards the peripheral chambers for the same volumetricsystolic contraction of the ventricle itself. In an attempt tocompensate for the reduced efficiency, the left ventricle tends tobecome dilated so as to increase the volume of blood pumped. However,the dilation of the ventricular chamber also results in a dilation ofthe annulus of the mitral valve, in addition to a deformation, andtherefore malfunctioning, of the sub-valvular apparatus thereof, whichtends to aggravate the lack of competence of the mitral valve itself,thereby increasing the regurgitated proportion and further reducing thepumping efficiency of the ventricle. Therefore, it is evident how theattempt to compensate for the mitral regurgitation via a dilation of theventricle results in an increase of the regurgitation itself andtherefore a triggering of a vicious circle which rapidly leads to theoccurrence of cardiac insufficiency (heart failure). This outlook isfurther aggravated by the fact that the increase in the volume of theventricle for diastolic purposes and the simultaneous thinning of theventricle wall increases significantly the level of stress undergone bythe cardiac muscle during the systolic phase (so-called afterload),quickly generating a state of suffering and weakening of the myocardiumwhich contributes to the deterioration of the condition of cardiacinsufficiency.

In the current state of the art, the standard therapy for the treatmentof severe insufficiency of a cardiac valve is the implantation of apermanent valve prosthesis or the repair of the native valve, whichmethod is often associated with the simultaneous implantation of deviceswhich promote the recovery of the functionality of the valve itself,such as, for example, rings for annuloplasty, artificial tendinous cordsin the case of atrio-ventricular valves, etc. In both cases, the therapyis usually applied by way of an open-heart surgical procedure whichaffords the cardio-surgeon direct access to the malfunctioning valve.Generally, the procedure requires the temporary arrest of the heart andthe production, by means of suitable pumps and oxygen exchangers, of anartificial extra-corporeal blood circuit which is capable of extractingvenous blood from the patient, oxygenating it and reintroducing it backinto the arterial circulation. Notwithstanding the refinement of thetechniques for controlling the cardiac arrest and the improvement in theeffectiveness levels of the extra-corporeal circulation systems, theinvasiveness of the open-heart treatment is a significant risk factorand the mortality associated with the surgical procedure is still high.For this reason, in many cases the general conditions of the patient,for example, the advanced age thereof or the presence of concomitantpathologies, thereby make the risks of mortality high, or of high levelsof invalidity associated with the conventional surgery to be consideredto be unacceptable. Therefore, the patient is refused surgicaltreatment, preventing access to a therapy which is essential for theresumption of the functionality of the valve and consequently theefficiency of the cardiac muscle.

In order to limit or even eliminate the risks and the disadvantages ofthe surgical procedure, innovative procedures for implantation with lowinvasiveness have recently been developed as alternatives to theconventional surgical therapies.

Initially, the reduction of invasiveness has been sought by reducing thedimensions of the surgical aperture for access to the cardiac valve withthe use of prostheses which do not require stitching at the implantationsite (so-called sutureless valve prostheses) and with the use ofsurgical instruments which are compatible with endoscopic typeprocedures.

More recently, there have been developed valve prostheses which areradially collapsible and which can be implanted by means of low-profilecatheters which are capable of navigating inside the vascular system andof releasing the prosthetic device by reaching the implantation site byremote access. This new technology has made it possible to carry out theimplantation of the replacement valve prosthesis with the heart beating,that is to say, without any need for cardiac arrest and extra-corporealblood circulation.

Independently of the procedure followed, whether it be a surgical ortranscatheter procedure, the sudden elimination of the regurgitation ofan atrio-ventricular valve, as obtained following a corrective procedureor replacement, involves a specific risk as a result of the similarlysudden increase of the haemo-dynamic load undergone by the ventricleduring the systolic discharge phase. Taking, for example, for the sakeof simplicity of exposition, the mitral valve, a significantregurgitation in the atrium via the incompetent mitral valve reduces thehaemo-dynamic load undergone by the left ventricle during the systolicdischarge, it being the atrium directly connected to the pulmonarycirculation and therefore characterized by low pressure systems. Aneffective correction of the mitral incompetence, with the totalelimination of the reflux in the atrium, therefore brings about a suddenincrease in the load undergone by the ventricle and therefore an abruptincrease in the force applied to the cardiac muscle. In the presence ofhaemo-dynamic conditions which are already critical and/or involve adilated ventricle, this sudden overloading of the myocardial muscle maybe the cause of serious acute post-procedural complications.

Another set of problems which is specifically associated with thereplacement of the incompetent mitral valve with an implantable valveprosthesis via the transcatheter route and more generally with valveprostheses which do not require the production of surgical sutures atthe implantation site, results from the expansion of the dimensions ofthe annulus of the mitral valve which is a consequence of the dilationof the cardiac chambers at the left-hand side of the heart caused by themitral regurgitation according to the mechanism described above. Mostknown mitral valve prostheses of the transcatheter type are based on theexpansion of a central element inside the valve opening. The main bodyof the prosthesis during the implantation moves from a compressedconfiguration which is necessary for the introduction and positioning ofthe prosthesis to an expanded configuration which is intended to producecontinuity with the native mitral annulus. Only contact with or at leastproximity to the native annulus ensures the correct functioning of theprosthesis, that is to say, suitable securing and para-valvulartightness with respect to backward flow.

Examples of transcatheter prostheses for a mitral valve which requireunder operating conditions radial dimensions which are congruent withrespect to those of the valve annulus are described in the documents WO2011/163275, WO 2010/037141 and WO 2011/002996, wherein a pair ofcircumferential rings of hooks in the first two documents and of loopsin the third document, respectively, produce a mechanism for engagementwith the annulus of the mitral valve. Other sets of inventive solutionswhich also require adaptation of the dimensions of the prostheses to thedimensions of the native annulus are described in WO 2008/103722,wherein a series of points and hooks are intended to become engaged bothwith the annulus and with the leaflets of the native valve, or in WO2014/138868, wherein the central member is even shaped in a “D”-likemanner in order to better fit the shape and dimensions of the mitralannulus.

It is worth underlining here how, in general, in the prior art it is thedimensions of the prosthesis which have to be adapted to the dimensionsof the dilated annulus, which necessity places a great limitation on theminimum profile to which the prosthesis itself can be collapsed in thepositioning and release catheter. A set of mitral valve prostheses ofthe sutureless type provided with a structure which interacts directlywith the annulus of the mitral valve is described in the document WO2014/080339. This document describes implantable prosthesis systemswhich include an annular element which is positioned at the level of theannulus so as to completely surround the native valve leaflets. Theexpansion inside the opening of a substantially cylindrical valve memberuntil it is brought into contact with the above-mentioned annularelement allows stabilization of the annulus, because the native leafletsremain fixed in position between the two components of the prostheticsystem near the insertion line thereof in the annulus itself. This knownsolution, unlike the other designs described above, has thecharacteristic of securing in a stable manner the annulus of the nativevalve to itself.

Statement of Invention

An object of the present invention is to solve the problems of the priorart. It should be noted that it is of great use and benefit for apatient affected by valve insufficiency to provide an implantablereplacement prosthesis, in particular if it is of the sutureless type,advantageously capable of bringing about in a gradual manner over timethe elimination of the valve regurgitation. The prosthesis which isdescribed below is also directed towards the production of an inverseremodeling action, that is to say, a constrictive action for reducingthe dimensions, of the native valve annulus dilated by the cardiacpathology. Inter alia, the possibility of applying such inverseremodeling of the annulus would also allow the simultaneous reduction ofthe dimensions of the prosthesis itself, overcoming one of thedisadvantages of the prior art.

Therefore, an object of the invention is to correct the pathologicalregurgitation of a cardiac valve, in particular an atrio-ventricularvalve, having the object of complete elimination of the valveinsufficiency according to a gradual transition over time, which allowsbetter adaptation of the muscle of the ventricular wall to the newworking conditions and therefore the reduction of the incidence of somecomplications directly associated with the valve replacement. Anotherobject of the invention is to provide a mechanism which makes theimplantable valve prosthesis capable of applying a corrective action tothe anatomy of the malfunctioning native valve, combating thedegenerative and dilative effects of the pathology.

Some aspects of the solution according to specific embodiments of theinvention are described, for the sake of clarity of description, withreference to the prosthetic system illustrated in the patent document WO2014/080339, the content of which is incorporated herein by reference.However, it is evident that in general terms the invention may also beapplied to valve prostheses having a different configuration from thatdescribed in this patent document and that they are adapted to thetreatment of the insufficiency of any cardiac valve, independently ofthe position thereof. In fact, any prosthetic system which includes astructure or a group of structures capable of being connected in asecure manner to the annulus of the cardiac valve to be treated maybenefit from the adoption of the present invention. In particular,though not exclusively, the invention may be applied to valve prostheseshaving the characteristics described in the patent documents WO2012/063228 and WO 2015/118464, the content of which is alsoincorporated herein.

According to a first aspect of the invention, a prosthesis for a cardiacvalve comprises prosthetic leaflets which are intended to functionallyreplace the native leaflets of a cardiac valve following theimplantation of the cardiac prosthesis, and further comprises aprosthetic member on which there are mounted the prosthetic leaflets andwhich is intended to take up a stable, predetermined functionalconfiguration in which the prosthetic member and the prosthetic leafletsreproduce the functionally correct configuration for the purpose of thephysiological replacement of the native cardiac valve. The prostheticmember is preconfigured so as to be fixed in an altered temporaryfunctional configuration, in which the prosthetic member has a deformedgeometry with respect to the above-mentioned stable, predeterminedfunctional configuration. The prosthetic member is preconfigured so asto move gradually during use from the altered temporary functionalconfiguration to the stable, predetermined functional configuration.

Advantageously, the gradual change of the prosthetic member from thealtered temporary functional configuration to the stable, predeterminedfunctional configuration can be carried out by resilient return.

According to a specific aspect, the prosthesis for a cardiac valve maycomprise retention members of the prosthetic member in the alteredtemporary functional configuration. Those retention members are providedfor gradual dissolution after the implantation of the cardiac prosthesisso as to allow the change of the prosthetic member from the alteredtemporary functional configuration to the stable, predeterminedfunctional configuration. Advantageously, the retention members may beof bio-erodible or biodegradable material.

According to a specific aspect, the prosthetic member may comprise amain support member for the prosthetic leaflets and an annularperipheral abutment member which is capable of surrounding the mainsupport member and against which the main support member can expand withsuch a radial force as to trap during use the native leaflets of thecardiac valve between it and the annular member. Advantageously, theannular abutment member can move from an altered temporary configurationto a stable, predetermined configuration and is provided to entrain withit the main support member of the prosthetic leaflets in order togenerally define the corresponding configurations, an altered temporaryfunctional configuration and a stable, predetermined functionalconfiguration, of the prosthetic member as a whole, respectively.Advantageously, the annular abutment member in the altered temporaryconfiguration can be resiliently deformed and/or extended with respectto the stable, predetermined configuration thereof. According to aspecific aspect, the annular abutment member can be resiliently retainedin the altered temporary configuration by the above-mentioned retentionmembers. Advantageously, the retention members can be inserted intocavities of the annular abutment member. According to a variant, theretention members may comprise a matrix, in which at least a portion ofthe core of the annular abutment member is incorporated.

According to a specific aspect, the deformation of the annular abutmentmember in the altered temporary configuration may be anisotropic.Advantageously, the annular abutment member may comprise at least onecontinuous ring in order to make the annular member deformable andinextensible. Advantageously, the annular abutment member may compriseat least two continuous rings which are axially spaced apart in order tomake the annular member deformable only in the plane of the annularabutment member.

According to a specific aspect, the cardiac prosthesis is generallycollapsible in a non-functional configuration with a small spatialrequirement which is capable of implantation by means of techniques ofthe transcatheter type.

The invention also relates to a method for producing a prosthesis for acardiac valve. That method advantageously comprises the steps of:

-   -   providing a prosthesis for a cardiac valve comprising prosthetic        leaflets which are intended to functionally replace the native        leaflets of a cardiac valve following the implantation of the        cardiac prosthesis, and a prosthetic member on which there are        mounted the prosthetic leaflets and which is intended to take up        a stable, predetermined functional configuration in which the        prosthetic member and the prosthetic leaflets reproduce the        functionally correct configuration for the purpose of the        physiological replacement of the native cardiac valve,    -   geometrically deforming the prosthetic member and fixing it in        such a manner that it takes up an altered temporary functional        configuration with a deformed geometry with respect to the        stable, predetermined configuration, preconfiguring it in such a        manner that it can move gradually during use from the altered        temporary functional configuration to the stable, predetermined        functional configuration.

According to a specific aspect of the above-mentioned method, theprosthetic member may be resiliently deformed geometrically and fixed inthe altered temporary functional configuration by means of retentionmembers which are gradually dissolvable during use.

In general terms, the solution in accordance with one or moreembodiments of the invention is based on the operation of deforming,preferably in a resilient range before implantation, the structure whichis mechanically connected to the valve annulus and stabilizing thatdeformed configuration in a temporary manner so that the deformationinterferes with the behaviour of the prosthesis for a predetermined butlimited period of time following the implantation of the prosthesis. Thedeformed configuration of the structure has to be such as to bring aboutthe partial incompetence of the prosthetic device. For anatrio-ventricular valve, for example, the prosthetic system has, for alimited period of time immediately after the implantation, a predefineddegree of incompetence, that is to say, of intra-prostheticregurgitation, capable of partializing the sudden increase of thesystolic load undergone by the ventricle associated with the eliminationof the valve insufficiency. Once a given period of time has elapsed,possibly determined, at least in principle, at the design stage, thepreferably resilient return of the material which composes the annularelement brings about the recovery of the correct geometry thereof andthe elimination of the anomalous deformation imposed on the prostheticdevice. This last effect therefore involves the disappearance of theincompetence of the prosthetic leaflets and the intra-prosthetic valveregurgitation.

In addition to the above-mentioned effect, the deformation which istemporarily imposed may bring about an increase in the dimensions of theportion of the structure which during the implantation method carriesout the connection to the native annulus and interacts therewith. Inthis manner, the structure and therefore the entire prosthetic systemare suitable for being implanted in an annulus having dimensions greaterthan those which would be compatible with the same prosthetic system buthaving the structure without the deformation imposed.

Downstream of the implantation method, in a period of time which may befrom a few days up to several weeks, the constraint which brings aboutthe deformation imposed on the structure gradually dissolves, allowingthe recovery of the true geometry and/or the dimensions of thestructure, and therefore the entire prosthetic system, in theimplantation system. The disappearance of the constraint for deformingthe structure cancels the incompetence of the valve prosthesis togetherwith a reduction of the dimensions of the valve annulus. There isthereby obtained the elimination of the valve insufficiency in a gradualmanner, with a less traumatic effect on the myocardial muscle, and aninverse remodeling of the annulus of the native valve.

It is evident that the two functional properties described above, thatis to say, the capacity for making the correction of the valveregurgitation gradual and the capacity for reducing the dimensions ofthe annulus, do not necessarily have to be both present at the sametime. As will be described below, in fact, it is possible to produce thegradual nature of the correction of the insufficiency withoutnecessarily producing the inverse remodeling of the annulus. Thisbehaviour may be required if the dilation of the valve annulus is notclinically appreciable.

More specifically, a solution in accordance with an embodiment of theinvention is compatible with a prosthetic system which comprises anannular element which is capable of being positioned at the rear of theleaflets of the native intra-ventricular valve, so as to surround itcompletely, and a central valve member which is collapsible to adiameter which is substantially less than that of the implant and whichis capable of expanding inside the mitral opening. This solution makesprovision for the annular element which is part of the prosthetic systemto include a core which is generally but not necessarily produced frommetal material which has in toto or even only partially a meshed form,or a helical form, or any geometry which allows the resilientdeformation thereof both in extension, that is to say, in thelongitudinal direction (obtaining the increase of the axial extent ofthe annular element, that is to say, the overall length), and withrespect to the plane in which the annular element is located, that is tosay, in a transverse direction (obtaining the variation of shape of theannular element). During the construction step of the component, thestructure is deformed in accordance with degrees of freedom which areallowed by the configuration thereof and in any case not beyond theresilience limit of the material from which it is composed, in order toensure the resilient return thereof to the natural configuration oncethe constraint which maintains it in the deformed configuration isremoved. By way of example, the annular element may be deformed byincreasing the axial extent thereof or by imposing an ovalized geometryor in any case a geometry which is different from the one expectedduring the normal operation condition, or by applying the twodeformations at the same time. An annular element modified in thismanner achieves the double result both of making the prosthetic systemsuitable for the implantation in a native annulus having greaterdimensions, as a result of the increased circumferential extent andtherefore the equivalent diameter of the annular element, and ofbringing about the intra-prosthetic insufficiency in the implanteddevice. With regard to this last point, it may be observed that thecentral member of the prosthetic system, which element supports theprosthetic leaflets, is preferably constituted by a collapsible andexpansible frame, the expanded formation of which, once the prosthesisis implanted, is limited by the geometry, the dimensions and theresilient characteristics of the annular element which completelysurrounds it. In fact, during the implantation method, the centralmember expands until it is mechanically connected to the annularelement. The final configuration of the prosthesis is thereforedetermined by the result of the balance between the radial force appliedby the central member, the expansion of which remains limited andincomplete in any case, and the constraint constituted by the annularelement. The prosthetic leaflets which are supported by the centralmember have dimensions adapted to provide optimum coaptation andtherefore effective fluid-tightness with respect to the intra-prostheticregurgitation, at the expected final configuration of the implant. Byimposing an additional deformation on the annular element, as mentionedabove, the final formation of the central member is consequentlymodified, thereby being over-expanded or ovalized, or at any rate havinga form different from that expected under normal operating conditions,or as a result of the combination of the two deformations. As a finaleffect, the prosthetic leaflets are not connected to each other in anoptimum manner and are incompetent, and the valve prosthesis exhibitsintra-prosthesis regurgitation.

In solutions in accordance with the embodiments of the presentinvention, the deformed configuration of the annular element is fixed bysupplying material which is characterized by erodible or degradableproperties in contact with blood and/or under the physiologicalconditions of the human body. By way of an application example, withoutwishing to limit in any way the general nature of the invention, it ispossible to obtain the result of fixing the deformation of the annularelement by supplying bio-erodible material which suitably fills thecavities of the mesh or the helix which constitutes the core thereof, inaccordance with the configuration adopted, or by covering completely, oronly suitable portions of, the structural elements of the core, andtherefore stiffening it in the deformed configuration thereof. Once theprosthesis is implanted, the bio-erodible material which is added forfixing the deformed configuration of the annular element comes intocontact with the haematic fluid and begins the process of degradationthereof. This bio-erosion results in a progressive reduction of thecapacity of the filler material to interfere with the annular elementwhich similarly therefore gradually recovers a configuration ofresilient equilibrium only with the central member, without anysuperimposition of a deforming effect as a result of the fillermaterial. By way of example, if there have been applied both theabove-described deformations to the annular element, it begins to reducethe circumferential extent thereof, producing an action involvinginverse remodeling, that is to say, contraction, of the native mitralannulus and at the same time allows a recovery of the circularity of thecentral member. The two combined effects return the intended coaptationto the prosthetic valve leaflets, eliminating the intra-prosthesisregurgitation which is exhibited by the device during the acutepost-implantation period.

The rate of degradation of the bio-erodible filler material may besufficiently predetermined by way of the chemical composition and thephysical characteristics of the material itself. In this manner, it ispossible to adjust the time required for the prosthesis to recover theconfiguration thereof which is functionally stable during operation. Itis thereby possible to establish a priori the transient period overwhich the left ventricle recovers full haemodynamic load which isassociated with the total elimination of the mitral insufficiency.

In solutions according to one or more embodiments of the presentinvention, the core of the annular element may be produced from anybiocompatible metal alloy, such as, for example, titanium alloys, whichare already characterized by a wide clinical experience in similarapplications. However, it appears to be advantageous, under generalconsideration of the necessary functional requirements required by thesutureless implantation technologies and even more so by transcatheterimplantation technologies, to use super-resilient alloys, that is tosay, those which allow great deformations while remaining in a resilientrange, that is to say, without being subjected to permanent distortions.An example of a super-resilient alloy already in use for sutureless andtranscatheter valve prostheses is the nickel-titanium alloy which hasequal atomic percentages and which is commercially known under the nameNitinol.

With regard to the fixing material for the deformed configuration of theannular element, in the current prior art there are known variousmaterials of the bio-erodible or biodegradable type, that is to say,biocompatible materials which are capable of being degraded under thephysiological conditions of the human body and in contact with thehaematic flow. Examples of materials with those characteristics arepolymers based on polylactic acid, polydioxanone acid (PDS),polyglycolic acid (PGA) or the copolymers thereof, wherein the additionof other monomers, such as, for example, lactic acid or trimethylenecarbonate, allows adjustment of the degradation and solubility rate inaccordance with the relationship between the various monomers used inthe synthesis and the nature itself of those monomers. Those polymersare available in various forms which allow different types of use forthe purposes of the present invention. For example, polyglycolic acid isalready used for producing surgical suture threads which can bere-absorbed. In embodiments of the present invention, there are providedre-absorbable threads which can be wrapped about the core of thedeformed annular element so as to fill, for example, the cavitiesthereof present in the configuration of the structure, therebytemporarily preventing the resilient return thereof and actually fixingit in position in the altered or deformed temporary configuration. Thereare also known bio-erodible materials which are used to producebiodegradable medical devices which can be implanted, such as screws,plates, etc. Those materials can be used in the present invention inorder to produce members such as inserts, wedges and the like, which areshaped so as to fill the cavities of the core of the annular element,thereby securing it in the altered or deformed temporary configuration.In other embodiments of the present invention, the bio-erodible materialmay form a matrix in which at least a portion of the core of the annularelement can be incorporated so as to be retained in the altered ordeformed configuration. In many cases, in fact, bio-erodible polymershave good mechanical characteristics: PGA fibres, for example, arecharacterized by a value of Young's modulus of approximately 7 GPa, thatis to say, ten times greater, for example, than high-densitypolyethylene (HDPE).

In the scope of the various embodiments of the present invention, thedeformation or alteration temporarily imposed on the annular element inorder to achieve the advantages described above may also apply only tosingle portions of the annular element itself and the entire structurethereof.

Similarly, the present invention may also be applied according to thesame principles to annular structures which are subdivided into aplurality of segments which are physically separated from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The solution in accordance with one or more embodiments of theinvention, as for other characteristics and the relevant advantages,will be better appreciated with reference to the following detaileddescription which is given purely by way of non-limiting example andwhich is intended to be read together with the appended Figures, inwhich for simplicity corresponding elements are indicated with identicalor similar reference numerals and the explanation thereof is notrepeated. In this regard, it should be expressly understood that theFigures are not necessarily drawn to scale (with some details which canbe exaggerated and/or simplified) and that unless indicated otherwisethey are simply used to conceptually illustrate the structures andmethods described. In particular in the drawings:

FIGS. 1A and 1B show in configurations corresponding to different stepsof the implantation method general schematic representations of aprosthetic device for the treatment of cardiac valves, in accordancewith a configuration compatible with the embodiments of the presentinvention;

FIGS. 2A, 2B show as a perspective view and plan view the two componentsof the prosthesis illustrated in FIGS. 1A and 1B, respectively;

FIG. 2C shows the assembled configuration of the components of FIGS. 2Aand 2B;

FIGS. 3A, 3B and 3C describe the same components of the prostheticdevice both in the separated and in the assembled configuration, whereinit is assumed that the annular element is temporarily deformed in thedirection increasing the circumferential extent thereof longitudinally,with the recovery of the correct operational configuration once thecause of the deformation has been eliminated;

FIGS. 4A, 4B and 4C describe the same components of the prostheticdevice both in the separated and in the assembled configuration, whereinit is assumed that the annular element is temporarily deformed in thedirection of ovalization of the shape, with the recovery of the correctoperational configuration once the cause of the deformation has beeneliminated;

FIGS. 5A and 5B show another version of the components of the prostheticdevice which is for the treatment of cardiac valves and which isdescribed in FIGS. 1A and 1B, both in the separated and in the assembledconfiguration, having different geometries from a circular geometry;

FIGS. 6A, 6B and 6C show the same components of the prosthetic devicedescribed in FIGS. 5A, 5B and 5C, both in the separated and in theassembled configuration, wherein it is assumed that the annular elementis temporarily deformed both by increasing the circumferential extentthereof and by varying the shape thereof, with the recovery of thecorrect operational configuration once the cause of the deformation hasbeen eliminated;

FIGS. 7A and 7B show an example of a construction solution of the coreof the annular element in accordance with an embodiment of the inventionwhich allows a deformation thereof both in terms of an increase in thelongitudinal extent and in terms of a variation in shape;

FIGS. 8A and 8B show a different construction solution of the core ofthe annular element in accordance with an embodiment of the inventionwhich also allows a deformation thereof both in terms of an increase inthe longitudinal extent and in terms of a variation in shape;

FIGS. 9A and 9B describe a technique for fixing the deformedconfiguration of the core of the annular element by means of blocks ofbio-erodible material which are forcibly inserted in the meshedstructure;

FIGS. 10A and 10B show a different construction solution of the core ofthe annular element in accordance with an embodiment of the inventionwhich allows only the deformation in terms of variation of shape, beinga longitudinally inextensible geometry;

FIG. 11 describes a technique for fixing the deformed configuration ofthe core of the annular element by means of blocks of bio-erodiblematerial which are forcibly inserted in some openings of the structure;

FIGS. 12A and 12B show a different construction solution of the core ofthe annular element in accordance with an embodiment of the inventionwhich illustrates a variant with respect to the solution described inFIGS. 10A and 10B in order also to allow the deformation of the core interms of longitudinal extension; and

FIGS. 13A and 13B describe a technique for fixing the deformedconfiguration of the core of the annular element by means of inserts ofbio-erodible material which are forcibly connected in the structure ofthe core.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A and 1B schematically illustrate two different steps of theimplantation method of a prosthesis 10 for a cardiac valve according tothe present invention, which prosthesis is used to replace thefunctionality of a native atrio-ventricular valve V to be treated. Theprosthesis 10 comprises a first component in the form of an annularelement 12 and a second component in the form of a central member 14,which supports prosthetic valve leaflets 16. During the implantationmethod, the annular element 12 is positioned outside the nativeatrio-ventricular valve V in order to completely surround it, while thecentral member 14 is expanded inside the same native atrio-ventricularvalve V (FIG. 1A). The expansion of the central member 14 causes the twocomponents 12, 14 to be connected to each other (FIG. 1B). The contactbetween the two components 12, 14 is not direct but instead occurs withthe interposition of the leaflets L of the native valve V which remaininterpolated between the two components 12, 14. As a result of theflexibility and deformability of the native atrio-ventricular valve V,the final configuration of the prosthesis 10 is determined mainly by thebalance of the mutually exchanged forces during the interaction betweenthe two components 12, 14 and is a function of the resilient return ofeach of the two components 12, 14. In particular, if the annular element12 is substantially inextensible or at least mainly rigid in acircumferential direction, that is to say, in the longitudinaldirection, with respect to the exchanged forces, the central member 14expands as far as the radial dimension allowed by the length of theinternal circumference 12 a of the annular element 12. The configurationof final equilibrium, that is to say, post-implantation, of theprosthesis 10 is therefore predictable and controllable, because thecontribution of the native valve in terms of structural interaction issubstantially negligible. The diagram described in FIGS. 1A and 1B ispurely indicative of the principle of basic operation of the prosthesis10, and in the context of that construction solution there can beprovided different solutions. For example, the annular element 12 can beopen and/or subdivided into a plurality of portions in order to allowready positioning thereof around the native atrio-ventricular valve V.

The annular element 12 is then re-closed and/or re-assembled before theexpansion of the central member 14. There can further be providedflexible arms for connection between the annular element 12 and thecentral member 14 in order to keep the mutual positioning stable andpredefined between the two components 12, 14 during the implantationsteps of the prosthesis 10. Furthermore, the final configuration of theprosthesis 10 may provide for a circular or oval or D-like opening inaccordance with the requirements of the configuration considered, forexample, to reproduce a general geometry which is mainly similar to thenative atrio-ventricular valve V.

FIGS. 2A, 2B and 2C schematically illustrate examples of the two maincomponents 12, 14 of the prosthesis 10. Different configurations of thecomponents or the prosthetic system as a whole do not influence theapplicability and the efficiency of the present invention and theconstruction solutions thereof described herein below. In particular,FIG. 2A shows perspective views of the annular element 12, in the leftof the Figure, and the central member 14, on the right of the Figure.FIG. 2B illustrates the same two components 12, 14 as a plan view, inwhich there can clearly be seen the prosthetic valve leaflets 16 whichare supported by the central member 14.

With reference to FIG. 2B, the internal diameter D1 of the annularelement 12 is less than the external diameter DD of the central member14 at the maximum expansion thereof, that is to say, in the absence ofany external constraint, measured at the cross-section at which the twocomponents are mechanically connected together. The interference whichexists between the internal diameter D1 of the annular element 12 isless than the external diameter DD of the central member 14, causingduring use the radial expansion of the central member 14 to be stoppedagainst the constituted constraint of the annular element 12, generatinga contact pressure which is substantially continuous over all thecontact surface between the two components 12, 14 so as to make theconnection thereof stable and at the same time blocking the nativeleaflets V, which are interpolated between the two components 12, 14 ina functionally stable configuration of the prosthesis 10. The prostheticvalve leaflets 16 which are supported inside the central member 14 aredimensioned so as to have in the functionally stable configuration ofthe prosthesis 10 optimum mutual coaptation. In the functionally stableconfiguration of the prosthesis 10, that is to say, when the centralmember 14 is expanded as far as the diameter and in the configurationswhich are determined by the radial constraint produced by the annularelement 12 which surrounds it, the prosthetic valve leaflets 16 have thecapacity for completely sealing the opening of the prosthesis 10 duringclosure in order to eliminate any backward flow, as shown schematicallyin FIG. 2C, which illustrates as a plan view the two components 12, 14in the characteristic assembled configuration of the implantedprosthesis 10.

In the configuration of maximum possible expansion of the main member14, as can be seen on the right in FIG. 2B, the prosthetic valveleaflets 16 are incompetent and therefore the closure of the valve isinsufficient. According to an aspect of the present invention, thecentral member 14 is allowed to expand to a greater extent and/or inaccordance with a different geometry from that provided for in thefunctionally stable configuration of FIG. 2C so that the coaptationbetween the prosthetic valve leaflets 16 is intentionally partial and inany case insufficient over a transient time period. Therefore, theprosthesis 10 is affected during the operation thereof under thosetemporary conditions which are altered with respect to the functionallystable configuration by a degree of intra-prosthetic incompetence, thatis to say, by a backward flow through the opening, proportional to thewhole of the deformation to which the central member 14 is subjectedwith respect to the functionally stable configuration thereof, that isto say, with respect to the optimum operating condition.

FIGS. 3A, 3B and 3C show the prosthesis 10 in which the annular element12 has at least for a limited period of time an internal diameter D2which is dimensionally intermediate between the internal diameter D1which is capable of retaining the central member 14 in the functionallystable configuration and the external diameter DD which the samecompletely expanded central member 14 would assume without any externalconstraint. As illustrated in FIG. 3B, the assembled prosthesis 10 hasan expansion of the central member 14 which is limited by the annularelement 12 which winds round it, with the two components 12, 14connected to each other at a diameter of equilibrium which is greaterthan the optimum one of the functionally stable configuration as in FIG.2C. Consequently, the coaptation during closure between the prostheticvalve leaflets 16 is also insufficient (FIG. 3B) and a centralregurgitation opening R remains present inside the aperture with thevalve closed. The pre-dilation of the annular element 12 to acircumferential extent greater than that provided for by the optimumconnection between the two components 12, 14 determines the loss ofsealing capacity with inverse flow at the side of the prosthesis 10,which is therefore incompetent. If the deformation of the annularelement 12 were permanent, the prosthesis 10 would be stably incompetentin terms of the in-vivo operation thereof. If, however, the annularelement 12 is capable of gradually recovering the longitudinalelongation thereof over time, over a similar transient period theregurgitation will also tend to decrease as far as being eliminated. Atthe end of this transient period, the valve prosthesis 10 will acquirefull competence with respect to inverse flow during in-vivo operationthereof in accordance with the optimum configuration thereof, which isfunctionally stable, illustrated in FIG. 3C.

FIGS. 4A, 4B and 4C illustrate a prosthesis 10 in which the annularelement 12 assumes at least for a limited period of time a geometricshape which is different from the one provided for functionally suitablestable operation of the implanted prosthesis 10. The example set out inFIG. 4A, shows, with simple non-limiting explanatory purpose of thegeneral nature of the invention, the annular element 12 which isdeformed to an ovalized geometry with a smaller diameter D3 and greaterdiameter D4. Generally, the internal circumference 12 a of the annularelement 12 has a length equivalent to the circumference of the diameterD1 of FIGS. 2A and 2B. In other words, the annular element 12 shown inFIG. 4A is substantially obtained by means of ovalization of the annularelement 12 which is shown in FIGS. 2A and 2B. In general, it is possibleto impose a deformation which is also different from the oval shape, aswill be shown below. The result of the deformation of the annularelement 12 is schematically shown in FIG. 4B, wherein the assembledsystem which represents the implanted configuration of the prosthesis 10also shows an ovalization of the central member with a resultantdistortion of the prosthetic valve leaflets 16 and loss of thecoaptation during closure. The deformation in terms of shape of theannular element 12 therefore allows the solid connection between the twocomponents 12, 14 of the prosthesis 10, but does not bring about at thesame time the incompetent closure, with the appearance ofintra-prosthesis regurgitation. In that case too, if the deformation interms of shape is temporary, that is to say, if the annular element 12is capable of recovering over time the functionally correct shapethereof, the prosthesis 10 as a whole will also gradually recover theappropriate closure of the prosthetic valve leaflets 16, beingcompletely competent at the end of the transient period, as indicated inFIG. 4C.

The alterations of length and shape of the annular element 12 describedabove with reference to FIGS. 3A and 4A may also be appliedsimultaneously, resulting in a combination of an increase in thecircumferential extent of the annular element and a variation in termsof shape thereof. Via this combination of deformations, which aretemporary and reversible according to the techniques already describedabove, there is obtained at the same time the corrective constrictioneffect, that is to say, of inverse remodeling, of the dilated annulus ofthe native pathological atrio-ventricular valve V, to which the annularelement 12 is connected during the implantation step, and the temporaryincompetence effect of the prosthesis 10, which advantageously allows arisky sudden increase of the haemodynamic load undergone by theventricular muscle immediately after the prosthesis 10 is implanted tobe prevented.

The examples set out in the preceding Figures are purely indicative andare not intended to be limiting in terms of the possible constructionsolutions which can be adopted by the present invention. By way ofexample, FIGS. 5A and 5B show a different and more general constructionsolution of the prosthesis 10 according to the present invention. FIG.5A is a plan view of the two separate components 12, 14, setting out howthe annular element 12 and the central member 14 may have geometrieswhich are different from each other and both not necessarily beingcircular. The annular element may have, as illustrated on the left inFIG. 5A, a substantially “D”-like shape which is very similar to theanatomical shape of the annulus of an intra-ventricular valve V and istherefore particularly suitable for being connected thereto during theimplantation method. The central member 14 may instead have a generalovalized shape, with an asymmetrical configuration of the prostheticvalve leaflets 16, which is optimized to produce the correct coaptationin the final assembled configuration. FIG. 5B shows the assembledconfiguration of the prosthesis 10, as results from the resilientequilibrium reached between the two components following the expansionof the central body 14, which is initially collapsed inside the annularelement 12. Since this configuration of equilibrium is substantiallydetermined during the design phase of the prosthesis 10, because theeffect of the apparatus of the native valve V is at a minimum, it isalso possible to configure the system of prosthetic leaflets 16 so thatthey are completely competent, that is to say, without anyintra-prosthetic opening during closure, in the implanted, functionallystable configuration illustrated in FIG. 5B.

FIGS. 6A, 6B and 6C show a different embodiment of the presentinvention. FIG. 6A illustrates the separate components 12, 14 of theprosthesis 10. The annular element 12 is deformed both in terms of thedimensions, that is to say, with a greater circumferential extent, andin terms of the shape, which is circularized. FIG. 6B shows the effectof the deformation which is imposed on the annular element 12 in thefinal configuration of the assembled prosthesis 10, which is differentin terms of shape and dimensions from the stable configurationassociated with the correct operation of the prosthesis. The opening Rwhich is produced in the aperture as a result of the lack of coaptationbetween the prosthetic valve leaflets 16 is responsible for theintra-prosthetic backward flow, making the prosthesis 10 incompetent. Ifthe deformation applied to the annular element 12 is temporary andreversible, according to the principles of the invention describedabove, with a transient time period which is determined by the rate ofbio-erosion of the fixing component of the deformed configuration, theprosthesis 10 recovers the stable configuration thereof for normaloperation with smaller radial dimensions and correct coaptation betweenthe prosthetic valve leaflets 16. In this case, therefore, theprosthesis 10 is also capable both of producing a contraction andremodeling the annulus of the native intra-ventricular valve V and ofgradually eliminating the valve incompetence by progressively increasingthe haemodynamic load undergone by the ventricle.

FIG. 7A and FIG. 7B show according to two different perspective views,for a better understanding of the drawing, a schematic illustration ofone possible geometry of the core of the annular element in accordancewith an embodiment of the invention. The core is substantially producedin a three-dimensional helical shape. A similar geometry can be obtainedusing a metal thread, which is pre-formed and optionally connected tothe ends thereof for greater stability of the structure, or on the basisof a curved tube so as to form a closed figure, optionally with themutually welded head ends, and in which the helical geometry is producedby cutting the wall in a suitable manner, for example, by laser cutting.The material from which the core is composed may generally be a metal ora metal alloy, for example, a titanium alloy. In particular, for devicesin the field of transcatheter technologies in humans there isadvantageously used nickel/titanium alloy, which is commercially knownas Nitinol, as a result of the super-resilient property thereof, whichallows great deformations while remaining within the range of resilienceof the material, as well as for the biocompatibility thereof. As aresult of the axial extensibility and the flexional deformability, thestructure shown in FIG. 7 may be temporarily deformed both in terms ofexpansion, that is to say, increase of the axial length, and in terms ofmodification of the shape, advantageously filling the cavity between thecontiguous helixes with a bio-absorbable or bio-erodible materialaccording to the technique already described above.

FIG. 8A and FIG. 8B illustrate another version of the core of theannular element in accordance with a different embodiment of theinvention. FIG. 8A shows the core as a whole while FIG. 8B shows thedetail of a portion thereof. In the construction solution shown here,the core is substantially constituted by a meshed toroidal structure. Inthis case, the structure may also be constructed both by means of afabric of interwoven metal threads and by starting from a tube bent soas to form a ring, which is optionally but not necessarily closed, onthe wall of which there are produced suitable openings by means of lasercutting. This last method is particularly advantageous, allowingvariation as desired of the thicknesses of the arms of the mesh, as wellas the dimensions, the shape and the position of the various openingsformed in the wall of the tubular element. In this manner, there isprovided a great freedom of configuration in order to freely adjust theresilient return of the core and therefore of the annular element inaccordance with the requirements of the project. Simply by way ofexample, the resilient return of the core may be varied in accordancewith the position, it being possible to construct regions which are morerigid and regions which are more flexible, or there can be obtainedanisotropic behaviour of the structure both as a whole and only locally,which allows, for example, provision of a flexible core for deformationsinside the plane but extremely rigid with respect to deformationsoutside the plane.

The materials which can be used are obviously the same as theconstruction solution described above.

Independently of the resilient characteristics which are conferredthereon, the meshed structure described in FIG. 8 affords thepossibility similarly to the structure in FIG. 7 of increasing the axialextent thereof, of being deformed in accordance with different shapeswith respect to the initial shape, and having both deformationssuperimposed.

According to an embodiment of the present invention, the deformedconfiguration may be fixed for a predetermined period of time by meansof co-moulding of bio-erodible or biodegradable material above thesuitably deformed core, for example, inside a mould, in order to producea covering which maintains the distorting effect on the structure of thecore. The co-moulding may involve all the core or also only limitedportions of the core, in accordance with the particular deformationwhich it is desirable to achieve, or the resilient characteristics whichit is desirable to preserve in the core including in the deformedconfiguration.

Another construction method, which is illustrated in FIG. 9A and FIG.9B, provides for the use of inserts, such as wedges or blocks ofbio-erodible material which are suitably shaped and dimensioned andwhich are forcibly inserted in the openings present in the mesh. Inparticular, FIG. 9A shows, as a reference for the following Figure, anon-deformed portion of the structure of the core described in FIG. 8.FIG. 9B shows, by way of non-limiting example of the general nature ofthe invention, how blocks of bio-erodible material which are suitablyoverdimensioned are capable of fixing a deformed configuration if forcedinside the openings of the mesh of the structure of FIG. 9A. Assumingthe more general case, in which the openings of the mesh have differentdimensions from each other, if the criterion of over-dimensioning ofeach block as a function of the dimensions of the opening inside whichit is forced is kept constant over the whole structure, the effect whichis obtained is a homothetic expansion thereof. In other words, if thepercentage of interference between the block and the opening is keptconstant independently of the position on the structure, there isgenerally obtained the effect of increasing the axial extent of thestructure without a substantial deformation of shape thereof, asindicated in FIG. 9B. If, however, the percentage of interference variesin accordance with the position, there is also obtained a variation ofshape of the ring. For example, if the percentage of interference isgreater for the openings in the internal face with respect to that inthe external face, the radius of curvature of the axis of the structureincreases (straightening effect). If, on the other hand, the percentageof interference is greater for the openings in the external face, theradius of curvature of the axis decreases (bending effect). It isevident that, by way of an application example, by applying astraightening effect (percentage of interference greater in the internalface) to two diametrically opposed portions and a bending effect(percentage of interference greater in the external face) to twodiametrically opposed portions which are also orthogonal to thepreceding ones, there is obtained the ovalization of a core which isinitially circular or, as a specific case, the circularization of a corewhich is initially oval. It is also evident that it is possible toobtain only the deformation of the geometry of the core withoutincreasing the axial extent thereof, producing the straightening effector the bending effect by means of insertion of blocks in a single faceof the structure rather than in both.

In light of the multiplicity of the possible positions of the openingsin a meshed core similar to the one illustrated in FIG. 8, it may beimmediately understood how extensive and varied is the range ofdeformations of the structure which can be obtained by means of theforced insertion of blocks or wedges of bio-erodible material which issuitably shaped and dimensioned. With the deformation being imposed inthe resilient range, optionally with the use of super-resilient alloyssuch as Nitinol, the degradation which occurs in the human physiologicalfield of the material from which the blocks are produced leads over timeto the disappearance of the distorting effect and the recovery of theoriginal geometric and mechanical characteristics of the core andtherefore of the annular element.

FIG. 10A and FIG. 10B show another version of the core of the annularelement, in accordance with a different embodiment of the invention. Thestructure illustrated in FIG. 10A in its entirety and in FIG. 10B indetail for greater clarity of the configuration of the structure differsin terms of function from the one shown in FIG. 7 and in FIG. 8 becauseit is substantially inextensible longitudinally but only geometricallydeformable. In fact, notwithstanding the large number of openings whichare also formed in this configuration in the wall of the tube and whichmake it flexible, the presence of at least one continuous ring whichjoins the various sub-elements of the structure makes the structureinextensible in terms of axial extent. The presence in the structure ofa single continuous ring allows deformations of the core inthree-dimensional space. However, the presence of two rings which arediametrically positioned on the upper face and lower face or moregenerally spaced apart from each other axially as shown in FIG. 10,limits the degree of deformability of the structure in the plane.Therefore, this construction solution which may be necessary if theabsolute non-extensibility of the annular element is required during thenormal operating mode of the implanted prosthetic system, allows adeformed but non-expanded configuration. The geometric deformation maybe temporarily fixed by means of surrounding the core, or only portionsthereof, inside a covering of bio-erodible material, or by means ofinsertion of suitable spacers or blocks, which are produced from thesame bio-erodible material and which are forced inside the openings ofthe structure. Merely by way of example, without wishing to limit thegeneral nature of the invention, FIG. 11 shows the variation of shape,from circular to oval, imposed on the structure described in FIG. 10 bymeans of the forced insertion of blocks of bio-erodible material in somespecific openings of the structure, which are selected in accordancewith the desired modification to the local radius of curvature of theaxis of the structure.

FIG. 12A and FIG. 12B show a variant of the configuration of the core ofthe annular element which is described in FIG. 10 which also againintroduces the possibility of deforming the structure in a longitudinaldirection, increasing the circumferential extent thereof, in addition tovarying the shape thereof. In general, the introduction of deformableand extensible elements as constituting portions of the rings whichcharacterize the configuration of FIG. 10 also allows the extensionthereof in the axial direction. In the construction solution describedin FIG. 12, the introduction of “S”-shaped elements, as clearlyillustrated in FIG. 12B, introduces the additional degree of freedomgiven by the possibility of a dilation in the direction for increasingthe circumferential extent of the core.

In the case of the construction solution described in FIG. 12, thedeformed configuration may also be temporarily fixed by means ofco-moulding bio-erodible material only in some suitably selectedportions of the core, or by means of blocks and wedges which areproduced from the same bio-erodible material and which are suitablydimensioned and forcibly introduced inside the openings formed in thewall of the initial toroidal structure. In addition, the constructionsolution in FIG. 12 allows any deformed configuration also to be blockedonly by interfering, with a bio-erodible material, with the geometry ofthe “S”-like connection. As an example of a non-limiting constructionsolution of the general nature of the invention, FIG. 13A and FIG. 13Bshow in accordance with different perspectives for greater clarity ofexposition, inserts of bio-erodible material which are provided withpins which are dimensioned and spaced apart so as to be able to beembedded in a forced manner between the arms of the “S”-like portionwhich joins the various sub-elements of the structure, suitablymodifying the geometry thereof. The modification of the geometry broughtabout by the block may have both a component of dilation, in the case inwhich the increase of the spacing is produced between the ends of the“S”-like portion, and a component of modification of the shape, in thecase in which the variation of the equivalent radius of curvature of theportion is forced. The first action therefore has the effect ofincreasing the total circumferential extent of the structure while thesecond action has the effect of modifying the shape thereof. With regardto this last aspect, it should be emphasized that the anti-symmetry ofthe “S”-like shape allows both an increase and a decrease of theequivalent radius of curvature in accordance with which pair of arms isspaced apart to the greater extent. The effect of increasing thecircumferential extent and the distorting effect of the shape aresubstantially independent of each other in the sense that the whole ofeach one can be imposed in an autonomous and non-correlated manner onthe whole of the other one.

Finally, in the context of the transcatheter technologies, this lastconstruction solution appears to be particularly advantageous becausethe pins generate a local constraint of the unilateral type, as a resultof which additional deformations of the structure, for example, formaking the profile of the component compatible with the assembly thereofon a release catheter, are also possible in the presence of the inserts.

Naturally, the principle of the invention remaining the same, the formsof embodiment and details of construction may be varied widely withrespect to those described and illustrated, without thereby departingfrom the scope of the present invention.

The invention claimed is:
 1. A cardiac prosthesis for a native cardiacvalve, comprising: prosthetic leaflets which are intended tofunctionally replace native leaflets of a cardiac valve followingimplantation of the cardiac prosthesis, a prosthetic member on whichthere are mounted the prosthetic leaflets and which is intended to takeup a stable, predetermined functional configuration in which theprosthetic member and the prosthetic leaflets reproduce a functionallycorrect configuration for physiological replacement of the nativecardiac valve, wherein the prosthetic member is preconfigured so as tobe fixed in an altered, temporary functional configuration, in which theprosthetic member is allowed to expand to a greater extent and/or toexpand to a greater extent in accordance with a different geometry fromthat provided for in said stable, predetermined functionalconfiguration, and so as to move gradually during use from the altered,temporary functional configuration to the stable, predeterminedfunctional configuration.
 2. The cardiac prosthesis for a native cardiacvalve according to claim 1, wherein the gradual movement of theprosthetic member from the altered, temporary functional configurationto the stable, predetermined functional configuration occurs byresilient return.
 3. The cardiac prosthesis for a native cardiac valveaccording to claim 1, comprising retention members of the prostheticmember in the altered, temporary functional configuration, the retentionmembers being provided for gradual dissolution after the implantation ofthe cardiac prosthesis so as to allow the movement of the prostheticmember from the altered, temporary functional configuration to thestable, predetermined functional configuration.
 4. The cardiacprosthesis for a native cardiac valve according to claim 3, wherein theretention members are of bio-erodible or biodegradable material.
 5. Thecardiac prosthesis for a native cardiac valve according to claim 1,wherein the prosthetic member comprises a main support member for theprosthetic leaflets and an annular peripheral abutment member which isadapted to surround the main support member and against which the mainsupport member can expand with such a radial force as to trap during usethe native leaflets of the cardiac valve between the main support memberand the annular peripheral abutment member.
 6. The cardiac prosthesisfor a native cardiac valve according to claim 5, wherein the annularperipheral abutment member moves from an altered, temporaryconfiguration to a stable, predetermined configuration and is providedto entrain with the annular peripheral abutment member the main supportmember of the prosthetic leaflets in order to define the altered,temporary functional configuration and the stable, predeterminedfunctional configuration of the prosthetic member.
 7. The cardiacprosthesis for a native cardiac valve according to claim 6, wherein theannular peripheral abutment member in the altered, temporaryconfiguration is resiliently deformed and/or extended with respect tothe stable, predetermined configuration thereof.
 8. The cardiacprosthesis for a native cardiac valve according to claim 7, wherein theannular peripheral abutment member is resiliently retained in thealtered, temporary configuration by retention members.
 9. The cardiacprosthesis for a native cardiac valve according to claim 8, wherein theretention members are inserted into cavities of the annular peripheralabutment member.
 10. The cardiac prosthesis for a native cardiac valveaccording to claim 8, wherein the retention members comprise a matrix,in which at least a portion of a core of the annular peripheral abutmentmember is incorporated.
 11. The cardiac prosthesis for a native cardiacvalve according to claim 5, wherein deformation of the annularperipheral abutment member in the altered, temporary configuration isanisotropic.
 12. The cardiac prosthesis for a native cardiac valveaccording to claim 5, wherein the annular peripheral abutment membercomprises at least one continuous ring in order to make the annularperipheral abutment member deformable and inextensible.
 13. The cardiacprosthesis for a native cardiac valve according to claim 12, wherein theannular peripheral abutment member comprises at least two continuousrings which are axially spaced apart in order to make the annularperipheral abutment member deformable only in a plane of the annularperipheral abutment member.
 14. The cardiac prosthesis for a nativecardiac valve according to claim 1, wherein the cardiac prosthesis iscollapsible in a non-functional configuration with a small spatialrequirement, adapted to be implanted by techniques of atranscathetertype.
 15. The cardiac prosthesis for a native cardiac valve according toclaim 1, wherein in the altered, temporary functional configuration theprosthetic member has a configuration which is more expanded withrespect to the stable, predetermined functional configuration, in whichthe prosthetic member has a configuration relatively more contracted.16. A cardiac prosthesis for a native cardiac valve, comprising:prosthetic leaflets which are intended to functionally replace nativeleaflets of a cardiac valve following implantation of the cardiacprosthesis, a prosthetic member on which there are mounted theprosthetic leaflets and which is intended to take up a stable,predetermined functional configuration in which the prosthetic memberand the prosthetic leaflets reproduce a functionally correctconfiguration for physiological replacement of the native cardiac valve,wherein the prosthetic member is preconfigured so as to be fixed in analtered, temporary functional configuration, in which the prostheticmember is allowed to expand to a greater extent from that provided forin said stable, predetermined functional configuration, and/or inaccordance with a different geometry, moving from one shape to anothershape while a perimeter thereof is not reduced in respect to thatprovided for in said stable, predetermined functional configuration, andso as to move gradually during use from the altered, temporaryfunctional configuration to the stable, predetermined functionalconfiguration.